The class encapsulates the ASN.1 DER encoding/decoding work
with the DirectoryString structure
(as specified in RFC 3280 -
Internet X.509 Public Key Infrastructure.
Certificate and Certificate Revocation List (CRL) Profile.
http://www.ietf.org/rfc/rfc3280.txt):
DirectoryString ::= CHOICE {
teletexString TeletexString (SIZE (1..MAX)),
printableString PrintableString (SIZE (1..MAX)),
universalString UniversalString (SIZE (1..MAX)),
utf8String UTF8String (SIZE (1..MAX)),
bmpString BMPString (SIZE (1..MAX))
}